In many internal combustion engines which are actually used for vehicles, a cylinder block and a cylinder head are separately (independently) casted, the cylinder block and the cylinder head are tightened by a plurality of cylinder head bolts.
Contrary to this, a patent document 1 discloses an internal combustion engine in which a cylinder head and a cylinder block are integrally casted. In the patent document 1, a water jacket is divided by a partition wall into a head side water jacket around a combustion chamber, and a cylinder side water jacket around the cylinder, so as to adequately adjust temperature distributions of the cylinder head side and the cylinder block side.
The head side water jacket is arranged to forcibly circulate the coolant from one end side of a cylinder row direction toward the other end side. Moreover, the cylinder side water jacket is connected to the head side water jacket through a through hole formed in the partition wall, and to circulate the coolant between the head side water jacket and the cylinder side water jacket by natural convection.
However, in the cylinder block disclosed in the patent document 1 in which there is provided the partition wall dividing the water jacket into the cylinder head side and the cylinder block side, a position of a knock sensor is not sufficiently considered. There is a room for improving the position of the knock sensor.